Absorbable metallic implants, such as stents, clamps, orthopedic implants, and many others are currently in use or are in development for medical purposes. The implants are inserted in the patient and are intended to perform a desired function over a given period of time, but are eliminated from the body without a further surgical procedure. The implants are therefore made of special absorbable alloys such as magnesium, iron, or zinc alloys, thus allowing the patient's body to degrade the implants over time so that ultimately they may be eliminated via the normal metabolism.
However, it is difficult to estimate the speed of the absorption process with sufficient accuracy, since this may vary from patient to patient. In clinical practice, however, it is important to know the state of degradation and the mechanical state (including the integrity) of the implants. Known methods such as X-ray, nuclear spin, ultrasound, intravascular ultrasound (IVUS), or optical coherence tomography (OCT) have only limited suitability for this purpose, since on account of the absence of spatial resolution and qualitative chemical selectivity they are not able to adequately image the transformation processes in the metal which sometimes occur at the microscopic and submicroscopic levels. Therefore, there is a need for a device which allows measurement of the state of degradation of absorbable metallic implants, and therefore of the proportion of the absorbed material and the mechanical integrity of the implants.